Experimental and computational investigation of supersonic impinging jets

The results of an experimental and computational study of a moderately underexpanded axisymmetric supersonic jet issuing from a converging nozzle and impinging on a ground plane are presented. The goal of this work is to develop a better understanding of the impinging jet flowfield, which is of significant practical interest because of its presence in short takeoff and vertical landing (STOVL) aircraft during hover as welt as in other aerospace-related and industrial applications. The experimental measurements include flow visualization, surface-pressure distributions, and velocity field data obtained using particle image velocimetry (PIV). The experimental data, especially the velocity field measurements, were used to verify the accuracy of computational predictions. Computational results obtained using two different turbulence models produced almost identical results. Comparisons with experimental results reveal that both models capture the significant features of this complex flow and were in remarkably good agreement with the experimental data for the primary test case. The experiments and computations both revealed the presence of the impingement zone stagnation bubble, which contains low velocity recirculating flow. Other features, including the complex shock structure and the high-speed radial wall jet, were also found to be very similar. The ability to measure and predict accurately the impinging jet behavior, especially near the ground plane, is critical because these are regions with very high mean shear, thermal loads, and unsteady pressure forces, which contribute directly to the problem of ground erosion in STOVL applications.